REFERENCE TO RELATED APPLICATION This application claims the right of priority based on U.S. provisional application Ser. No. 61/802,792, filed on Mar. 18, 2013, and the right of priority based on TW application Serial No. 102127373, filed on Jul. 30, 2013. The entire contents of each of these applications are hereby incorporated by reference.
BACKGROUND 1. Technical Field
The present disclosure relates to a light-emitting device, and in particular to a light-emitting device comprising a light-absorbing layer.
2. Description of the Related Art
The light-emitting diodes (LEDs) of the solid-state lighting elements have the characteristics of low power consumption, low heat generation, long operational life, shockproof, small volume, quick response and good opto-electrical property like light emission with a stable wavelength so the LEDs have been widely used in household appliances, indicator light of instruments, and opto-electrical products, etc.
A light-emitting diode usually comprises a light-emitting stack and two electrodes provided for injecting a current into the light-emitting stack for emit light. In general, two electrodes are design to have a current spreading throughout the light-emitting stack such that a light-emitting area configured to emit light is substantially the same as the surface area of the light-emitting stack. However, in other application, there is a need for a light-emitting having a limited light-emitting area with a high current density for improving light efficiency thereat.
SUMMARY OF THE DISCLOSURE The present disclosure provides a light-emitting device.
This light-emitting device comprises: a light-emitting stack, having a side wall, comprising an active layer emitting light; and a light-absorbing layer having a first portion surrounding the side wall and being configured to absorb 50% light toward the light-absorbing layer.
BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing is included to provide easy understanding of the application, and is incorporated herein and constitutes a part of this specification. The drawing illustrates the embodiment of the application and, together with the description, serves to illustrate the principles of the application.
FIG. 1 shows a top view of a light-emitting device in accordance with the first embodiment of the present disclosure.
FIG. 2 shows a cross-sectional view of the light-emitting device, taken along line AA′ of FIG. 1.
FIG. 3 shows a top view of a light-emitting device in accordance with the second embodiment of the present disclosure.
FIG. 4 shows a cross-sectional view of the light-emitting device, taken along line BB′ of FIG. 3.
FIG. 5A shows a top view of a light-emitting device in accordance with the third embodiment of the present disclosure.
FIG. 5B shows a cross-sectional view of the light-emitting device, taken along line XX′ of FIG. 5A.
FIG. 6 shows a top view of a light-emitting device in accordance with the third embodiment of the present disclosure.
FIG. 7 shows a top view of a light-emitting device in accordance with the third embodiment of the present disclosure.
DETAILED DESCRIPTION OF THE EMBODIMENTS To better and concisely explain the disclosure, the same name or the same reference number given or appeared in different paragraphs or figures along the specification should has the same or equivalent meanings while it is once defined anywhere of the disclosure.
The following shows the description of embodiments of the present disclosure in accordance with the drawing.
FIGS. 1 and 2 disclose a light-emitting device 100 in accordance with the first embodiment of the present disclosure. FIG. 1 shows the top view of the light-emitting device 100 and FIG. 2 shows the cross-sectional view of the light-emitting device 100. The light-emitting device 100 comprises a substrate 10, a light-emitting stack 13 formed on the substrate 10, a reflective layer 12 formed between the substrate 10 and the light-emitting stack 13, and a bonding layer 11 formed between the reflective layer 12 and the substrate 10. The light-emitting stack 13 comprises a first-type conductivity semiconductor layer 131, a second-type conductivity semiconductor layer 133, and an active layer 132 sandwiched between the first-type and second-type conductivity semiconductor layers 131, 133. The first-type and second-type conductivity semiconductor layers 131, 133 respectively provide electrons and holes such that electrons and holes can be combined in the active layer 132 to emit light when a current is applied thereto. The material of the light-emitting stack 13 comprises III-V group semiconductor material, such as AlxInyGa(1-x-y)N or AlxInyGa(1-x-y)P, wherein 0≦x, y≦1; (x+y)≦1. Depending on the material of the active layer 132, the light-emitting stack 13 is capable of emitting a red light with a wavelength in a range from 610 nm to 650 nm, a green light with a wavelength in a range from 530 nm to 570 nm, a blue light with a wavelength in a range from 450 nm to 490 nm or a UV light with a wavelength in a range from 400 nm-450 nm. A method of making the light-emitting stack 13 is not limited to but comprises Metal-organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE), Hydride Vapour Phase Epitaxy (HVPE), evaporation or ion electroplating. The light-emitting device 100 further comprises a first electrode 16 formed on the second-type conductivity semiconductor layer 133, a second electrode 17 formed on the substrate 10, a light-absorbing layer 18 formed on a portion of the first electrode 16, and an insulation layer 19 formed between the light-absorbing layer 18 and the second-type conductivity semiconductor layer 133. In this embodiment, the first electrode 16 is patterned and comprises an inner segment 161, an outer segment 162, and a plurality of extending segments 163 electrically connected the inner segment 161 with the outer segment 162. As shown in FIG. 2, the light-emitting device 100 further comprises an ohmic contact layer 15 formed between the inner segment 161 and the light-emitting stack 13 for providing an ohmic contact path therebetween. The ohmic contact layer 15 has a shape substantially equal to that of the inner segment 161. The ohmic contact layer 15 is not formed between the outer segment 162 and the light-emitting stack 13. Alternatively, the ohmic contact layer 15 can be formed between the outer segment 162 and the light-emitting stack 13, and has a shape substantially equal to that of the outer segment 162 (not shown). The inner segment 161 and the outer segment 162 comprise a circle, rectangle, quadrangle or polygon in shape. When the inner segment 161 and the outer segment 162 are a circle in shape, they are concentric.
Referring to FIG. 2, the second-type conductivity semiconductor layer 133 of the light-emitting stack 13 has a side wall 1331 and a top surface. The top surface has a first region 1332 and a second region 1333. The second portion 1333 is defined by the outer segment 162 formed on the first region 1332 such that the first region 1332 surrounds the second region 1333. Specifically, the outer segment of the first region 1332 surrounds the second region 1333. The inner segment 161 is formed on a portion of the second region 1333 without covering the entire second region 1333 so a partial second-type conductivity semiconductor layer 133 is exposed for the light emitted from the active layer 132 to pass outside the light-emitting device 100 therethrough. The exposed second region 1333 where there is no inner segment 161 disposed can be roughed by etching such as dry etching or wetting etching for improving light extraction. The light-absorbing layer 18 has a first portion 181 surrounding the side wall 1331 and a second portion 182 above the first region 1332 of the top surface of the light-emitting stack 13. Specifically, the insulation layer 19 and the outer segment 162 is formed on and covering the first region 1332 of the top surface of the second-type conductivity semiconductor layer 133 and the second portion 182 of the light-absorbing layer 18 is formed on and covering the insulation layer 19 and the outer segment 162. In addition, the insulation layer 19 covers the side wall 1331 of the light-emitting stack 13 and the first portion 181 covers a side wall of the insulation layer 19. Since the ohmic contact layer 15 is merely formed between the inner segment 161 and the light-emitting stack 13, the active layer 132 below the inner segment 161 (that is, the second region) emits light such that a first quantity of the light (more than 90%) directly passes outside the light-emitting device 100 through the second region 1333 and a second quantity of the light (less than 10%) may emit toward the light-absorbing layer 18 which is configured to absorb light. In one embodiment, more than 50% of the second quantity of the light is absorbed by the light-absorbing layer 18. In addition, the light emitted from the active layer 132 does not pass outside the light-emitting device 100 through the first region 1332 and the side wall 1331. A ratio of an area of the second portion 1333 to an area of the top surface of the light-emitting stack 13 is between 10%-90%, that is, a light-emitting area is defined as 10%-90% of the area of the light-emitting stack 13. The light-absorbing layer 18 can comprise a single layer or a plurality of sublayers and has a thickness larger than 300 Å. The light-absorbing layer 18 comprises titanium (Ti), chromium (Cr), nickel (Ni), or combinations thereof. The first electrode 16 comprises metal or metal alloy. The metal comprises Cu, Al, Au, La, or Ag. The metal alloy comprises La, Ge—Au, Be—Au, Cr—Au, Ag—Ti, Cu—Sn, Cu—Zn, Cu—Cd, Sn—Pb—Sb, Sn—Pb—Zn, Ni—Sn, or Ni—Co. The light-absorbing layer 18 can comprise a bonding pad for wire bonding to an external structure (not shown), for example, a submount, and therefore forming an electrical connection therebetween when in operation.
In this embodiment, the reflective layer 12 is embedded within the bonding layer 11 in a position corresponding to the second portion 1333 of the top surface of the light-emitting stack 13. Accordingly, when the light emitted from the active layer 132 emits toward the substrate 10, the light can be reflected by the reflective layer in opposite direction toward the second-type conductivity semiconductor layer 133. Since some of the light only passes outside through the second portion 1333 of the top surface of the second-type conductivity semiconductor layer 133, the reflective layer 12 has an area substantially equal to that of the second portion 1333 of the top surface of the light-emitting stack 13. In other embodiment, the reflective layer 12 can have an area substantially larger than that of the second portion 1333 of the top surface of the light-emitting stack 13.
FIGS. 3 and 4 disclose a light-emitting device 200 in accordance with the second embodiment of the present disclosure. FIG. 3 shows the top view of the light-emitting device 200 and FIG. 4 shows the cross-sectional view of the light-emitting device 200. The light-emitting device 200 has the similar structure with the first embodiment of the light-emitting device 100 except that the inner segment 161 has two inner sub-segments 1611, 1612. A plurality of first extending segment 1631 electrically connects the two inner sub-segments 1611, 1612 with the outer segment 162 and a plurality of second extending segments 1632 electrically connects one of the two inner sub-segments 1611, 1612 with the outer segment 162. The first extending segment 1631 and the second extending segments 1632 are alternately arranged. The outer segment 162 comprises a plurality of protrusions 164. The outer segment 162 and the protrusions 164 are provided for defining the second region 1333 where the light emitted from the active layer 132 merely passes outside the light-emitting device 200 therethrough. As shown in FIG. 4, the ohmic contact layer 15 is formed between the two inner sub-segments 1611, 1612 and the light-emitting stack 13 for providing an ohmic contact path therebetween. The ohmic contact layer 15 has a shape substantially same as that of the two inner sub-segments 1611, 1612 of the inner segment 161. The ohmic contact layer 15 is not formed between the outer segment 162 and the light-emitting stack 13. Alternatively, the ohmic contact layer 15 can be formed between the outer segment 162 and the light-emitting stack 13, and has a shape substantially same as that of the outer segment 162. The inner two sub-segments 1611, 1612 of the inner segment 161 and the outer segment 162 comprise a circle, rectangle, quadrangle or polygon in shape. When the two inner sub-segments 1611, 1612 of the inner segment 161 and the outer segment 162 are a circle in shape, they are concentric. A ratio of an area of the second portion 1333 to an area of the top surface of the light-emitting stack 13 is between 10%-90%. It is noted that numbers of the inner segment and the outer segments can be varied depending on the actual requirements. The larger the desired area of the second region where the light emitted from the active layer passes outside the light-emitting device therethrough, the more numbers of the inner segment and the outer segments are.
FIGS. 5A and 5B disclose a light-emitting device 300 in accordance with the third embodiment of the present disclosure. FIG. 5A is a top view of the third embodiment. FIG. 5A shows a cross-sectional view of the light-emitting device, taken along line XX′ of FIG. 5A. As shown in FIG. 5A, the light-emitting device 300 comprises a light-emitting area and an electrode area surrounding the light-emitting area. The light-emitting area is substantially arranged in a center of the light-emitting device 300. The electrode area is a light-absorbing area, or a non-light-emitting area. The light-emitting area has a shape of circle in top view. It is noted that the shape is not limited and can be polygon, such as triangle or square. Assuming the shape of the light-emitting area is a circle, its diameter is between 0.004-0.5 mm. In one embodiment, the diameter is between 0.001-0.2 mm. The light-emitting device 300 has a structure similar to the light-emitting device 100 of the first embodiment, except that the light-emitting device 300 comprises a trench 20 for separating an epitaxial structure 33 into a first semiconductor structure 22 and a second semiconductor structure 24. The first semiconductor structure 22 has a shape of circle in top view and the second semiconductor structure 24 surrounds the first semiconductor structure 22. The first semiconductor structure 22 and the second semiconductor structure 24 have substantially the same epitaxial structure 33 and have the same material composition and the same stacking structure. The epitaxial structure 33 comprises a first-type conductivity semiconductor layer 331, a second-type conductivity semiconductor layer 333, and an active layer 332 disposed between the first-type conductivity semiconductor layer 331 and a second-type conductivity semiconductor layer 333. The trench 20 separates the active layer 332 and the second-type conductivity semiconductor layer 333 of the first semiconductor structure 22 from the active layer 332 and the second-type conductivity semiconductor layer 333 of the second semiconductor structure 24. However, the first-type conductivity semiconductor layer 331 of the first semiconductor structure 22 and the first-type conductivity semiconductor layer 331 of the second semiconductor structure 24 are physically connected with each other. When the first semiconductor structure 22 is driven by a current, the active layer 332 of the first semiconductor structure 22 can emit a first light with a first main wavelength; and when the second semiconductor structure 24 is driven by a current, the active layer 332 of the second semiconductor structure 24 can emit a second light with a second main wavelength. The first main wavelength and the second main wavelength are within the same wavelength range. The first main wavelength and the second main wavelength have the same wavelength, for example, a red light having a wavelength of 610 nm-650 nm, a green light having a wavelength of 530 nm-570 nm, or a blue light having a wavelength of 450 nm-490 nm. In another embodiment, the first main wavelength can be different from the second main wavelength.
In order to avoid the first light from the active layer 332 of the first semiconductor structure 22 being emitted toward the second semiconductor structure 24, the trench 20 comprises one or more insulation layer. The insulation layer comprises an insulation material for absorbing the first light or reflecting the first light. The insulation material comprises an organic polymer material or inorganic material.
A reflective layer 12 of the light-emitting device 300 overlaying portions of the first semiconductor structure 22 is physically connected with the reflective layer 12 overlaying portions of second semiconductor structure 24. In a top view, the reflective layer 12 is configured to arrange at a position corresponding to the light-emitting area, and the reflective layer 12 has an area substantially equal to or larger than that of the light-emitting area. When the first light and/or the second light from the active layer 332 emits toward the substrate 10, the first light and/or the second light can be reflected toward the second-type conductivity semiconductor layer 333 and escape outward at a side near to the second-type conductivity semiconductor layer 333. Specifically, all the first light and/or the second light substantially emit outward from a top surface 33S of the light-emitting device 300. In one embodiment, the top surface 33S comprises a rough surface formed by etching or imprinting for improving the light extraction of the light-emitting device 300.
As shown in FIG. 5A, the electrode area comprises a plurality of external electrode structure. The plurality of external electrode structure substantially surrounds the second semiconductor structure 24 and comprises a first external electrode structure 28 and a second external electrode structure 38. Each of the first external electrode structure 28 and the second external electrode structure 38 can be a bonding pad for wire bonding to an external structure (not shown), for example, a submount, and therefore forming an electrical connection therebetween when driven by a current. The first external electrode structure 28 and a second external electrode structure 38 respectively comprise an insulation layer 19 and a conductive layer 281. The insulation layer 19 is disposed between the second semiconductor structure 24 and the conductive layer 281. A material of the conductive layer 281 comprises metal or metal alloy. The metal comprises La, Cu, Al, Au, or Ag. The metal alloy comprises GeAu, BeAu, CrAu, AgTi, CuSn, CuZn, CuCd, Sn—Pb—Sb, Sn—Pb—Zn, NiSn, or NiCo.
As shown in FIG. 5A, there are a pair of the first external electrode structure 28 and a pair of the second external electrode structure 38. The pair of the first external electrode structure 28 is disposed at opposite positions and facing each other and the pair of the second external electrode structure 38 is disposed at opposite positions and facing each other. In this embodiment, the first external electrode structure 28 and the second external electrode structure 38 are alternately arranged. In other embodiment, a number and an arrangement of the first external electrode structure 28 and the second external electrode structure 38 can be varied but not be limited to above description.
As shown in FIGS. 5A and 5B, the light-emitting device 300 comprises a plurality of extension electrode on the epitaxial structure 33. Specifically, the plurality of extension electrode comprises a first extension electrode 221 disposed on the first semiconductor structure 22 and a second extension electrode 241 disposed on the second semiconductor structure 24. The first extension electrode 221 or the second extension electrode 241 comprises a circular shape. However, a number and a shape of the first extension electrode 221 and the second extension electrode 241 can be designed to enhance current spreading.
As shown in FIG. 5A, the light-emitting device 300 comprises a first connecting electrode 223 connecting the first extension electrode 221 to the first external structure 28, and a second connecting electrode 243 connecting the second extension electrode 241 to the second external structure 38.
In one embodiment, the light-emitting device 300 can comprise an ohmic contact layer at a position corresponding to the extension electrode, for example among the first extension electrode 221, the second extension electrode 241 and the epitaxial structure 33. As shown in FIG. 5B, the light-emitting device 300 comprises a first ohmic contact layer 222 disposed between the first extension electrode 221 and the second-type conductivity semiconductor layer 333, and a second ohmic contact layer 242 disposed between the second extension electrode 241 and the second-type conductivity semiconductor layer 333. In another embodiment, the light-emitting device 300 can comprise an ohmic contact layer 362 disposed between the conductive layer 281 of the first external electrode structure 28 and the second-type conductivity semiconductor layer 333, and/or between the conductive layer 281 of the second external electrode structure 38 and the second-type conductivity semiconductor layer 333. The ohmic contact layers 222, 242 have the shape as substantially the same as the first and second extension electrodes 221, 241, respectively. By virtue of the ohmic contact layers 222, 242, 362, a contact resistance between the extension electrode and the second-type conductivity semiconductor layer 333 and a contact resistance between the conductive layer 281 and the second-type conductivity semiconductor layer 333 can be reduced.
As shown in FIG. 5B, the light-emitting device 300 comprises a lower electrode 37 formed on the substrate 10. The lower electrode 37 and the first external electrode structure 28 (or the second external electrode structure 38) are formed on opposite sides of the substrate 10, thereby forming the light-emitting device 300 with a vertical-type. In addition, since the first-type conductivity semiconductor layer 331 of the first semiconductor structure 22 and the first-type conductivity semiconductor layer 331 of the second semiconductor structure 24 are physically connected with each other, the lower electrode 37 can electrically connect with the first-type conductivity semiconductor layer 331 of the first semiconductor structure 22 and with the first-type conductivity semiconductor layer 331 of the second semiconductor structure 24 such that the first semiconductor structure 22 and the second semiconductor structure 24 can be synchronously driven when in operation. The substrate 10 is a conductive substrate and comprises a semiconductor material or a metal material.
As shown in FIG. 5A, the first external electrode structure 28 of the electrode area can function as a first electrode set cooperated with the lower electrode 37 for receiving a first current to form a current passage therebetween such that the first semiconductor structure 22 is driven to emit the first light with a first illumination; the second external electrode structure 38 different from the first electrode set can function as a second electrode set for receiving a second current to drive the second semiconductor structure 24 to emit the second light with a second illumination. The first illumination and the second illumination can be adjustable by the first current and the second current, or by a size of the first semiconductor structure 22 and the second semiconductor structure 24, for example, the area of the active layer of the first semiconductor structure 22 and the active layer of second semiconductor structure 24. When the area of the active layer of the first semiconductor structure 22 is smaller than the area of the active layer of second semiconductor structure 24, and a value of the first current is equal to that of the second current (the current density of the first semiconductor structure 22 is greater than that of the second semiconductor structure 24), the first illumination is greater than the second illumination. When the area of the active layer of the first semiconductor structure 22 is equal to the area of the active layer of second semiconductor structure 24 and a value of the first current is greater than that of the second current (the current density of the first semiconductor structure 22 is greater than that of the second semiconductor structure 24), the first illumination is greater than the second illumination.
The first electrode set and the second electrode set can separately and simultaneously receive a current. As shown in FIG. 5A, when only the first electrode set, i.e. the first external electrode structure 28 receives the first current, the first semiconductor structure 22 is driven to emit the first light. As shown in FIG. 6, when only the second electrode set, i.e. the second external electrode structure 38 receives the second current, the second semiconductor structure 24 is driven to emit the second light. As shown in FIG. 7, when the first electrode and the second electrode set, i.e. the first external electrode structure 28 and the second external electrode structure 38 separately receive the first current and the second current at the same time, the first semiconductor structure 22 and the second semiconductor structure 24 are driven to simultaneously emit the first light and the second light.
The foregoing description has been directed to the specific embodiments of this invention. It will be apparent to those having ordinary skill in the art that other alternatives and modifications can be made to the devices in accordance with the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure covers modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.
